Generally, the main components of a front hub assembly of a bicycle include a hub body, an axle extending through the hub body, anti-friction ball bearing structures which are positioned proximate the ends of the hub body to facilitate rotation of the body around the axle, and two cone nuts, one positioned on each end of the axle to hold the assembly together and the ball bearings against the hub body. All of these components are assembled together into a wheel hub and the hub bearings are properly adjusted with respect to the hub body by a bicycle hub manufacturer. At that point, the completed hub is ready to be assembled with the remainder of the front wheel components, such as the spokes and the rim, usually by a bicycle manufacturer.
A typical front hub body generally includes two flanges which are fixed to the ends of an intermediate tubular center section which holds the flanges spaced apart from each other. The two flanges are adapted to receive one end of numerous bicycle wheel spokes while the other ends of the spokes are fastened to the wheel rim. The hub flanges also serve as the outer or rotating hub bearing races which are operable to seat the ball bearings in proper position with respect to the hub body. A common, continuous bore passes through both of the hub flanges and the intermediate center section. The front axle of the hub assembly passes through the bore.
Many different designs and methods have been utilized for constructing the bicycle hub body. One such hub design is illustrated in the patent of Donnelly U.S. Pat. No. 448,509 which shows the entire hub body formed as a unitary structure. Another design involves constructing the hub body from two symmetrical components wherein each component consists of a flange and one-half of the intermediate center section. The two symmetrical components are then joined together by connecting the two ends of the two intermediate center sections such as by welding or another suitable attachment method. Still another hub body design utilizes three components including two flanges and a tubular center section. The two flanges are connected to opposite ends of the tubular center section to form the hub body, and examples of such a construction are shown in Samson U.S. Pat. No. 2,917,816 and Humlong U.S. Pat. No. 3,858,942. In the Samson patent, the components are designed so that there is an interference fit between the ends of the tubular center section and the mating bores in the two flanges. The components are forced together until the two ends of the tubular center section contact annular flanges or stops at the ends of the mating bores in the two hub flanges. In the Humlong patent, the diameter of each end of the tubular center section is reduced to provide a shoulder or stop for the two hub flanges to contact. During assembly, the reduced diameter on each end of the tube is inserted into a mating bore in each hub flange and are assembled onto the reduced diameter until they contact the shoulder or stop. Once the hub flanges are in contact with the shoulder, the outside ends of the reduced diameters on each end of the tubular center section are crimped or flared outwardly to secure the hub flanges to the tubular center section and to fix the position of the hub flanges with respect to the tubular center section and with respect to each other.
After the front hub body has been constructed and the front hub assembled, the hub is further assembled with other front wheel components to make a complete front bicycle wheel. The tubular center section of the hub body, in the completed wheel assembly, serves as a spacer to keep the two hub flanges a fixed distance apart and overcome forces on the wheel which tend to drive the two flanges together. For example, a portion of each flange serves as an outer rotating bearing race to hold the ball bearing structures of the hub assembly. As a result, various forces are transmitted to the flanges through these bearing races to generally force the two flanges toward each other in a direction parallel to the center line of the axle. The tubular center section operates to oppose these forces and thereby keeps the two flanges the correct distance apart on the bicycle wheel.
Wheel forces are also transmitted to each flange by the wheel spokes. On the front wheels of most bicycles, the spokes are arranged in an alternating crossing pattern. Each spoke in the wheel transmits a force to the hub flange, and the force can be divided into two vector components, one vector component is directed parallel to the front axle and tends to pull the two flanges toward each other as discussed above. These forces are opposed by the hub assembly, such as with shoulders or stubs at the ends of each tubular center section against which the hub flanges abut. The second vector component of the wheel force transmitted to the hub flanges by each spoke is in a direction tangential to the periphery of the hub flanges such that the spokes apply a torquing force to the hub flange. This torque tends to rotate the hub flanges in either a clockwise or counter- clockwise direction with respect to the tubular center section and with respect to each other depending upon the particular crossing pattern of the wheel spokes. Preferably, the number of spokes in each flange applying a clockwise torque would be equal to the number of spokes applying a counter-clockwise torque so that the torquing forces of the spokes offset each other.
However, during assembly of the bicycle wheel, the spokes are generally not tightened in unison. Instead, they are tightened individually in a predetermined sequence. Despite the efforts of the bicycle wheel assembler to tighten each spoke equally, there will generally always be a variation between the tension in one spoke versus the tension in another adjacent spoke in the wheel. As a result, the variations in spoke tension around the wheel cause variations in the forces transmitted to the hub flanges by the spokes, which, in turn, result in variations in the component of the force which applies a torque to the hub flanges. Oftentimes, as the spokes are tightened, a torquing force is applied to the hub flanges which is greater than the forces which the joint between the end of the tubular center section and the flange can withstand. As a result, the joint fails and the flange rotates with respect to this tubular center section. When the flange rotates, the distance between the holes for the spokes in that particular hub flange are changed with respect to the corresponding holes for the opposite ends of each spoke in the wheel rim. That is, the angular orientation of the hub flange with respect to the wheel rim is changed. Depending upon the spoke crossing pattern of the wheel, the distance between the hole in the hub flange and the hole in the rim for each spoke either increases or decreases. If the hub flange rotates a large amount and the hole distance changes significantly, the wheel assembly cannot be completed with the fixed length spokes available.
Therefore, it is desirable to prevent rotation of the hub flanges with respect to the center section and with respect to each other in a hub body in order to yield proper assembly of a bicycle wheel. To this end, it is desirable to construct a hub body with hub flanges that are able to withstand the torquing forces applied to the hub flanges. One way of increasing the strength of the joint between a flange and the center section is to weld or braze the joint. However, such an additional assembly process would make construction of the hub body more complex, and accordingly, more expensive.
Another possible method is to form irregularities along the circumference of the hub flange bore and then to force the flange onto the reduced end diameter of the tubular center section. Once assembled, the end of the tubular center section is crimped or flared to complete the joint and to secure the flanges to the center section. However, there is a limit to the amount of forced interference that can be used between the hub flange bore and the end of the tubular center section while still maintaining the integrity of the two components within the constructed hub body. This structural limit placed on the forced interference between the flange and the center section restricts the amount of torquing force which the joint is able to withstand. Therefore, there is still a need for a front wheel hub body construction which is able to withstand a sufficient amount of torquing force on the hub flange while maintaining the integrity of the joint and the construction of the hub body. Furthermore, there is a need for a hub body which may be constructed simply, efficiently, and at a relatively low cost while maintaining the sturdy construction of the hub.